This application relates to new electrically conductive polymeric materials, more particularly to compositions comprised of doped polyacetylene deposited throughout porous polymeric substrates, electrically conductive membranes, and methods for both the preparation and use of the foregoing.
Recently, polyacetylene has been successfully synthesized in the form of high quality uniformly thin flexible silvery-copper-colored polycrystalline films of cis-polyacetylene and silvery polycrystalline films of trans-polyacetylene, by polymerizing acetylene monomer in the presence of a Ti(OC.sub.4 H.sub.9).sub.4 --Al(C.sub.2 H.sub.5).sub.3 catalyst system, employing a critical catalyst concentration to avoid the formation of polyacetylene powder, and critical polymerization temperatures (temperatures lower than -78.degree. C. for obtaining the cis polymer, and temperatures higher than 150.degree. C. for obtaining the trans polymer). Polymerization temperatures between -78.degree. C. and 150.degree. C. result in the polymer having a mixed cis-trans structure. The details of the synthesis of these polycrystalline films of polyacetylene and their characterization are described in a series of papers by Shirakawa et al (Polymer Journal, Volume 2, No. 2, pages 231-244, 1971; Polymer Journal, Volume 4, No. 4, pages 460-462, 1973; Journal of Polymer Science, Part A-1, Polymer Chemistry Edition, Volume 12, pages 11-20, 1974; and Journal of Polymer Science, Part A-1, Polymer Chemistry Edition, Volume 13, pages 1943-1950, 1975), all of which are incorporated herein by reference.
The polycrystalline films of trans-polyacetylene and cis-polyacetylene described by Shirakawa et al, are both p-type semiconducting materials, but varying in room temperature electrical conductivity. The room temperature electrical conductivity of the trans-polyacetylene is typically about 4.4.times.10.sup.-5 ohm.sup.-1 cm.sup.-1, while that of the cis polyacetylene is typically about 1.7.times.10.sup.-9 ohm.sup.-1 cm.sup.-1, depending on the method of preparation.
It has also recently been found that by controlled chemical doping of polyacetylene in the form of a polycrystalline film, such as those described by Shirakawa et al, with a conductivity-increasing amount of an electron acceptor dopant and/or a conductivity-decreasing amount of an electron donor donant, it is possible to produce a whole family of p-type electrically conducting doped polyacetylene films whose room temperature electrical conductivity may be preselected over the entire range characteristic of semiconductor behavior and into the range characteristic of metallic behavior. Such doping procedure is described in U.S. Pat. No. 4,222,903, and is incorporated herein by reference. As disclosed in said U.S. patent, high levels of room temperature p-type electrical conductivity characteristic of or approaching metallic behavior, i.e., on the order of about 10.sup.-1 to about 10.sup.3 ohm.sup.-1 cm.sup.-1, can be achieved with a number of electron acceptor dopants, including bromine, iodine, iodine chloride, iodine bromide and arsenic pentafluoride, at dopant levels ranging from less than 0.001 to about 0.3 mol of dopant per --CH-- unit of the polyacetylene, with lower doping levels resulting in proportionally lower conductivity increases.
In U.S. Pat. No. 4,204,216 a method is disclosed for modifying the electrical conductivity of polycrystalline films of polyacetylene so as to provide at least a portion thereof with a preselected room temperature n-type electrical conductivity, by doping the polyacetylene with certain metal compounds.
Although the foregoing references adequately teach a means for producing polyacetylene films and for altering the eletrical conductivity of such films, a serious drawback exists in that the polyacetylene films are quite fragile and are thus very susceptible to mechanical shock. It is envisioned that in certain applications a membrane, such as a microporous membrane, may have particular advantages if it is also electrically conductive.